Navalny is implicitly barred from running for office because of a conviction in a fraud case which has been viewed as political retribution. He could have run if he was given a special dispensation or if his conviction was cancelled.

Incumbent Vladimir Putin is set to easily win a fourth term in office in the March 18 election, with his approval ratings topping 80 percent.

Over the past year, Navalny has mounted a grassroots campaign which reached out to the most remote corners of Putin's heartland.

Navalny, 41 is the most serious challenger that Putin has faced in all his years in power, and the court cases against him have been widely seen as a tool to keep him from running for office.

In a pre-recorded video message that was released minutes after the Election Commission handed down the decision, Navalny called on his supporters to boycott the vote.

"The procedure that we're invited to take part is not an election," he said. "Only Putin and the candidates he has hand-picked are taking part in it."

Central Election Commission chief Ella Pamfilova told Navalny ahead of its vote to bar him that "maybe we would be interested if you were running," but said the conviction doesn't allow the commission to put him on the ballot.

Speaking before the vote, Navalny told the commission that their decision to bar him would be a vote "not against me, but against 16,000 people who have nominated me, against 200,000 volunteers who have been canvassing for me."

While Putin is all but certain to win an easy victory, the Kremlin wants his performance to be as strong as possible and has been concerned by growing voter apathy.

Navalny's call for a boycott could hurt the Kremlin's hopes for boosting turnout.

The involvement of Ksenia Sobchak, a 36-year-old star TV host, could raise public interest in the race. While Sobchak has denied colluding with the Kremlin, she could attract some of Navalny's supporters and help boost attendance.

Sobchak criticized Navalny's call for boycotting the vote, saying Monday that the "election is the only way to change something, and boycotting them is inefficient and harmful."

She proposed that Navalny join her campaign if she gets registered for the race.

Other veterans of past elections — liberal Grigory Yavlinsky and ultranationalist Vladimir Zhirinovsky — are also running. Communists nominated a new face, Pavel Grudinin, director of a big strawberry farm just outside Moscow.